1. Field of the Invention
This invention relates generally to apparatus and method for measuring rotation during jet pump tensioning in a nuclear reactor pressure vessel.
2. Description of Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within restrainer brackets by a gravity actuated wedge. The inlet mixers are each held in place at the top end by a preloaded beam. To secure the assembly, the jet pump beam is assembled with a high preload, applied by installing the jet pump beam bolt with a hydraulic tensioner.
High static and dynamic jet pump flow loads on the inlet mixer can, under some conditions, such as insufficient beam preload, cause oscillating motion and detrimental vibration excitation in the jet pump. The resultant increased vibration levels and corresponding vibration loads on the piping and supports can cause jet pump component degradation from wear and fatigue. Extreme component degradation can require plant shutdown. To assure the required preload is maintained, the beam bolt is securely locked to prevent loosening after tensioning is completed. The locking device design and engagement actuation must not interfere with operation of the jet pump tensioner. Accordingly, breaker poles, typically 2 inch in diameter, are used to lower the jet pump tensioner onto the beam bolt. The breaker poles may be used to prevent and/or reduce wind-up over the approximately 80 ft of coverage. However, the heavy breaker poles generally require the use of an overhead crane to assembly and transport the tools to its proper location. Thus, the employment of the overhead crane is time consuming and a laborious task for operators.